Porous refractory



keiuueii May 4, 1948 UNITED- STATES PATENT OFFIC POROUS REFRACTORYCharles J. Kinzie, Youngstown,

and Eugene Wainer, Niagara Falls, N. Y., assignors to The Titanium AlloyManufacturing Company, New

York, N. Y., a corporation of Maine No Drawing. Original No. 2,341,561,dated Febru ary 15, 1944, Serial No. Application for reissue rial No.713,102

7 Claims.

This invention relates to the production of insulating refractories.More particularly, it relates to the production of porous insulatingrefractories, especially zircon refractories, bonded with suitablebonding agents. This application is a continuation in part of copendingapplications Serial No. 204,392, filed April 26, 1938, now abandoned,and Serial No. 256,928, filed February 17, 1939, now Patent No.2,220,411.

"In'the past it has been known to construct porous-refractories byincorporatin with a refractory material a suitable quantity of organicpore-forming material, together with a liquid, to form -'a homogeneousmass, and then burning out the pore-forming material by firing at a.high temperature. Among the pore-forming materials that have been usedare cork, sawdust, wood, etc. In the case of many of these refractorymaterials, the incorporation of such a pore-forming material has-beenfound to decrease the strength to such an extent as to render themcommercially of low value. In order to increase the strength ofrefractory mat'erials, whether porous or non-porous, it"is also'known toincorporate bonding agents of various kinds. Among the bonding agentswhich have been used are phosphoric acid, certain double zirconiumsilicates, certain zirconates, and others. These may be considered aspermanent bonding agents, that is, they serve to permanently bond therefractory although the bonding agent itself may in some cases beentirely removed. The

n green strength of the material, before firing, may f bein'creased bywhich is eliminated in d s not permanentl inanent bonding agents are ingeneral less refracf tory,or produce in the course of firing materialswhich are less refractory, base material itself. As many of these highlyrefra'ct'ory materials, such 1 chief'utility from the fact "extremelyhigh temperatures, it is thesmaller the quantity of bonding agent while$56111- attaining adding such materials as gelatin, the process offiring and bond the base. The perthan the refractory as zircon, derivetheir that they will withstand obvious that satisfactory strength, thebetter *"willbe the final result.

It is therefore an object of this invention to produce materials of highrefractoriness, high h -porosity and high strength. It is another objectItofincrease the refractoriness of such materials um'ut harmfullyaffecting the porosity and strength without Other objects will appearhereinafter.

335,626, May 16, 1940.

November 29, 1946, Se-

These objects are accomplished by thoroughly mixing a refractorymaterial, particularly a high temperature refractory material, with abonding agent and asuitable quantity of liquid to a homogeneousconsistency, then subsequently thoroughly mixing an organic pore-formingmaterial with this mixture, shaping the mass, drying and firing at anelevated temperature. It has been found, in accordance with thisinvention, that the incorporation of the pore-forming material after theremaining ingredients of the mass have been thoroughly mixed with eachother, produces greatly improved and unobvious results, as shownhereinafter.

For pore-forming material, there is used any granular organic solid oflow or no ash content. Among such materials are cork,'wood and coke.Petroleum coke, whether calcined or uncalcined, is a particularlydesirable material because of its controllably lowash content andrelatively slow rate of burning, which is conducive to accurate controlof the process, with the production of a highly uniform product. Cokealso has the advantage that it is applicable to ramming and pressingprocedures, while cork cannot be permanently pressed because of itselasticity, causing expansion when the pressure is released. In the caseof cork, it is preferred to use a material having' arelatively slowburning rate, since cork with a fast burning" rate tends to eliminatevolatile matter so rapidly as to create cracks and fissures duringfiring. The pore-forming material must be sized within definite limitsso as to produce ware containing definite pore size. It must be of asize wholly and considerably coarser than the constituent grains of therefractory mix itself, since pore-forming material of a size in the samerange" as the grainrefractory prevents grain to grain contact of therefractory in the green mix, with almost complete loss of bond onfiring, whereas pore-forming material much coarser than the grainsthemselves allows grain to grain refractory contact resulting in wellbonded final ware.- For example, where the refractory material is ofparticle size wholly-passing through an 80 mesh screen, pore-formingmaterial no finer than 30 mesh should be used where the refractory'material is of a p'articlesize wholly passing through a 200 mesh screen,Dore-forming material no finer than mesh be used.

For refractory material zircon is preferably used because .of its highrefractoriness. Other suitable high temperature refractories comprisesilicon carbide, refractory aluminum oxide, mullite, sillimanite,chromite, olovine, forsterite,

quartz or other forms of refractory silica, refractory clays,electrically fused zirconia, talc, feldspar, beryl, rutile, kaolin,spinel, kyani-te, thorium oxide, thorite, ceria, andalusite,baddeleyite, porcelaln. This list may be further amended by: the use ofeither synthetic or natural minerals, uncalcined, or in the raw state,or in the precalcined state. With silicon carbide the so-called firesand, which is silicon carbide containing some incompletely combinedsilica, may be used. The refractory aluminum oxides include bauxite,raw: or precalcined, gibbsite, and corundum, or-synthetic fused aluminumoxide. Olivine isused-ravk or'calcined sufiiciently to form forsterite.Quartz is used in the form of sand, ,gbBi fl'a as. calcined quartz whichhas. been previously and suitably heated above 1470 C. so as to ilormcristobalite. The refractory clays include the various types ofnon-plastic fireclays, the flint clays, the kaolins, etc. Theserefractory materials may be used alone, in combination with each .other,or in combinationwith zircomaftertransforming same into the properphysical state for casting. Either milled or granular refractorymaterial, or a mixture thereof; maybe used, although milled material ora mixture of milled and granular material is preferred.

For permanent bonding agent, a considerable variety of materials may beused: excellent bond for zircon ware is phosphoric acid; (H POl), whichbonds even coarse zircon grains very tightly at low temperatures, andexcellent porous'ware can be made by the use of phosphoricacid alone asa bond. However, the use of HgPGgalone as a. bond sufiers from theserious disadvantage in the high temperature range, sincePzQsbecomesvola tile below 3000 F. and results in a pronounced permanentweakening of the structure unless the refractory is composed entirelyof] finely milled material. Preferred bonding agents, either with zirconor with other refractory materials, are double silicates of zirconiumand certain other metals, and certain zirconates, asdisclosed andclaimed in Reissue Batent No. .1;2241 and copending applications SerialNos. 25fi,9 2 8,n o,w Patent No. 2,220,411, and 329,524, now Patent No.2,220,412, especially when, used in conjunction with phosphoric acid.Otherbondln' a ents that may be used are those, disclosed; and,claimedin copending application to Wainer andfiake, Serial No. 285,580,now Patent.No. 2 .26'I,772. To secure the best results, milledbondingaigentsarepreferred.

Any of the standard organic bindersmaybe used to produce green strength.It has been found that a 5% gelatin solution isthe'best forgeneralusage, particularly for zirconware.

The amounts of these various.,materials.. be varied within quitewide,limits, Thev amount of bonding agent should bekept aalowaspossible andstill secure the desired: strength, both be:- cause the bonding agentsuseda'rel generally more expensive than the refractory base, such as.zircon, andbecause they are less. refractory than mate.- rials such aszircon. In, general, theQrefractory base should comprise a major portion-(i. e, at least, 50%) by weight of.the ntire massmriontothe addition ofpore-formingimaterialr Whezrusing a combination of phosphoricacidandjhezirconates or double silicates of. zirconium another. metal,as disclosed, in Reissue,P,atent,No. 21,224 and copendingapplicationsserial Nos. 256.928,, now Patent No. 2,220,! 1.1, an(1,329?24, now, Batent. No. 2,220,412, as the bonding, egent-.,it,has.,been.found that lessthan 1.0. partaby w.eight. o$=.-H:RO(

and less than 15 parts by weight of zirconate or double silicate per 100parts of refractory base is adequate for most purposes, althoughmore'may be used if desired.

The phosphoric acid is ordinarily irsolutlon form, and this,togetherwith gelatin solution or] i other agent to secure greenstrength, and water,

if desired, comprises the liquid portion ofvzit'he mass. Sufiicienttotal liquid is employed to secure 5 the proper consistency, which mayvary from a viscous slurry to a paste, depending upon f moldingprocedure to be used, such as ramming, pressing, molding or otherdesired method-of shaping. The presence of the gelatin solution increases; theviscosity of a mass which would otherwise. be quite fluid.

All the above. ingredients (refractory base. bonding agent,- aqueousliquid, and green strength i,

bonding agent, if desired), except the pore- 013m ing material, arefirst thoroughly mixed together until a homogeneousmixture,.substantial1y out lumps, is formed. The porerf'orming, rial isthen folded in" or mixed. withth'a, to a uniform consistency. The.amount. forming material depends upon the Gk. sired. In practice, it hasbeen foundia porosity of to of total-'volumeis able andin. this case.the. pore-forming and other materials. removed. comprise from 70 to 75%of the volume ofjfih tire mass. The weight, of pore-formingfinatedotwill of course depend upon its density; case of calcined coke with. a.zircon. approximately 3 parts by weight. ofzircontdlftd Zbparts byweight of, coke has, been founder a 18.

The mass is next, molded into... the, remnant; shape, allowed to dry,and isthe'n, rem

ing. In order to burn out the porer formingmatqe xam-m1.

' 1000 grams of' -'200.jmesh purifledizircomflm grams ofmesh'purifiedgzirconesandt. 35' 87% H3PO4 solution (s er; 1.71). maizeas 5%, gelatin solution,v are thoro gh ye ta gether to ahomogeneousjconsistencxa of; 10+30 mesh ca1cined. .petroleu1n,. thenmixed therewith until:- distriblitedl throughout the mass. The massunder pressure, dried andfired in standard refractoryprocedure inmiebdioxidiu atmosphere to 1800 is. when, temperature: above 2800 F..are usedthe PzQswillgslwlsjM till off so as to leave. the residual.mecmtidztig bondedin theform of a cellular brick mixv produces wareof7.0 to. 15%;poros1tg 3 is suitable for the temperatureirangefiilfialgm4000 F. It weighs approximately once-bait; of a similarly sized brickfrom.

isomitted.

Examine-2 2 treated as in Example 1,

- The table below shows the quantities EXAMPLES 3-19 In the followingExamples 3-19, all them- ,gredients except the coke are thoroughly mixedtogether to a homogeneous consistency. The coke is then mixed therewithuntil evenly distributed throughout the mass. The mass is then shapedunder pressure, dried and fired in accordance with standard refractoryprocedure in a good oxidizing atmosphere to 1800 F. (Examples 1-12, 18)or 2400" F. (Examples 13-47, 19) These mixes produce were of 70 to 75%porosity, and are suitable for the 2600 to 4000 F. range. and kinds ofingredients in the various examples.

600 grams calcined petroleum coke (size in mesh) 877 HQPOOJ solution(sp. gr. 1.71)

Other bonding agent (see below for kind) -200 mesh zircon 5% gelatinsolution The other bonding agent in Examples 3, 4 and 13 may be milledsodium zirconium silicate, potassium zirconium silicate or lithiumzirconium silicate; in Examples 5, 6 and 14 it is milled calciumzirconium silicate; in Examples 7, 8 and 15 it may be milled bariumzirconium silicate, magnesium zirconium silicate, zinc zirconiumsilicate or a fired equimolecular mixture of clay and zirconia powder;in Examples 9, 10 and 16 it is a 4 to 1 milled mixture of calciumzirconium silicate, with either sodium zirconium silicate, potassiumzirconium silicate, lithium zirconium silicate, zinc zirconium silicate,barium zirconium silicate or magnesium zirconium silicate; in Exampleslland 1'? it is milled T102 or SnOa; in Example 12 it is milled ZrOz orThO2; in Examples 18 and 19 it may be the zirconate of either lithium,sodium, potassium, calcium, magnesium, zinc or barium.

EXAMPLE 20 50 parts of mesh refractory material (zircon, quartz,aluminum oxide, silicon carbide, rutile, fused zirconium dioxide,mullite, sillimanite, olivine, forsterite, chromite, refractory clay,kaolin, beryl, spinel, lryanite, thorium oxide, thorite, ceria,feldspar, andalusite, talc, baddeleyite, porcelain, raw or synthetic,calcined or uncalcined, or mixtures thereof), 44 parts of 200 meshmilled refractory material as above, 8 parts of 87% HBPO; solution (sp.gr. 1.71) 5 to 10 parts of calcium zirconium silicate or other bondingagent, 15 to 20 parts of water and 1 part of oxalic acid (which may beomitted if desired) are thoroughly mixed to a homogeneous consistency.500 grams of this mass is then mixed with 500 cc. of 10+20 mesh granularcoke, cork or wood. until the latter is evenly distributed throughoutthe mass. The mass is then shaped, dried and fired to 1800 to 2400 F.,depending 6 upon the refractory used and the degree of reifractorin'essdesired.

EXAMPLE 21 ExArarLs 22 3000 grams of 200 mesh zircon, 90 grams of sodiumzirconium silicate and 550 cc. of 5% gelatin solution were thoroughlymixed to a homogeneous consistency and screened through a 20 meshscreen. 2400' cc. of cork were then'mixed therewith until uniformlydistributed throughout the mass with the formation of a smooth paste.The mass was then shaped into the form of a brick, dried and fired to2500 F.

Refractory materials prepared in accordance with the present inventionhave been observed to exhibit strengths which were quite unexpected, ascompared with similar refractory materials prepared by mixing all theingredients at the same time, including the pore-forming material. Thismay be accounted for in part by the fact that the pore-forming materialpartially prevents intimate contact between the bonding'agent and therefractory base, if it is added before the refractory base and bondingagent are thoroughly intermingled. For comparative purposes, refractorybricks were constructed as follows, following the procedure of Example22 as closely as ,possible except for the time at which the poreformingmaterial wasadded.

with difficulty. The mass was rammed so as to secure approximately thesame density as in Example 22. The mass was dried for the same period oftime as in Example 22 and was then fired simultaneously and side by sidein a furnace with the brick of Example 22 and for the same period oftime.

The same procedure was followed as in A except that the ramming wasomitted.

The brick of Example 22 and brick A were of approximately the samedensity, but were both about 1.6 times as dense as brick B. Certainstrength tests were then applied to all three bricks. The cross-breakingand crushing tests used were the same or patterned after the recommendedprocedures of the A. S. T, M., except that, due to the small size of thetesting equipment, a smaller test specimen was used throughout (for testprocedures see 1939 Book of A. S. T. M. Standards, part II, Non-metallicmaterials-constructional, page 198).

The cross-breaking test equipment is provided with suitable bearings sothat full contact is made with the specimen at all times. A specimen 4%inches long by 1 inch wide by 1 inch deep is used. The is positioned-onthe bearingsv e a t y a pictured on page 200 or: therabovereierence. Theload is. applied to the top knife edge by means of a lever'arm, and theload continually increased by pouring sand into a bucket held by thelever arm at a specified position on said arm.

The modulus. of rupture (cross-breaking strength) in pounds per squareinch is reported as calculated, by the following formula:

where R=modulus of rupture in pounds per square inch W=total load inpounds at which specimen failed l'=distance between support in inchesb=width of specimen in inches d=depth of specimen inlinches By means ofthe above test the modulus of ruptureof the three test. bricks are asfollows: Example 2-2:,3120 pounds. per squareinch A=2250pounds persquare inch 15:17 pounds per square inch The crushing strength wasdetermined using the familiar recording Carver Laboratory hydraulicpress.- A bearing'block was used for perfeet positioning of the-specimenas shown on page 199 of the above reference. Check runs were made onspecimens varying in cross sectional area from 0.75 in. to 16 in Loadwas impressed at the rateof about 1000 pounds per minute, loading beingstopped at first instance of failure.

The cold crushing strength in pounds per square inch was calculated-fromthe formula:

where S=cold crushing strength in pounds per square inch W=total loadindicated by testing machine A=average of the gross areas of topandbottom ofthe specimen, in square inches, of the section ofthespecimen perpendicular to the line of appllcation of the load. Y

By means of the above test the cold crushing strengths of the threebricks are:

Example 22:2170 pounds per square inch A=320 pounds persquare inchB=63=pounds per'square inch The invention and the advantages thereofhavingbeen' described, it is understood that it is not intended to belimited, except as definedin the appended claims,

We claim: v

l. The method ofmaking a refractory structure of high porosity whichcomprises thoroughly mixing---a refractory base witha permanent bondingagent including a double-silicate of zirconium and a metal taken fromthe'group consisting of lithium, sodium, potassium, magnesium, calcium,bariumand'strontium'in the presence of an aqueous-liquid, subsequentlyadding to the batch a 2., The method" ofjmakin'g arefracto y structureof' ighporositi; which,compr ses ro shly mixins av refractory base witha permanentbondin a ent includin phosphoric. acidand a. double, s ili-.

atje of zirconium and a metal taken. from the.

r p consisting, of. lithium, sodium, potassium. magnesium. calcium,barium and strontium and a green strength bonding, agent in the presenceof an aqueous. liquid, subsequently adding to the batcha. granularorganic solid, shaping, the mass, drying, and firing at an, elevatedtemperature.

3; The method of makinga, refractory structure of high porosity whichcomprises thoroughly mixing zircon with a permanent bonding agent in thepresence of an aqueous liquid, subsequently adding to the batch agranular organic-solid, shaping the mass, drying, and firing at anelevated temperature.

4.. Themethod of making a refractory structure of high porosity whichcomprises, thoroughly mixing zircon with a permanent bonding agent inthe presence of an aqueousliquid, subsequently add ing to the batch agranular organic solid havin particle, sizes larger than the particlesizes of said zircon and said bonding agent, shaping the mass, dryingand firing at an elevated temperature uptier-good oxidizing conditions.

5. The method of making a refractory structureofhigh.v porosity whichcomprises thoroughly mixing zircon with a permanent bonding agent,including a, double. silicate of zirconium and ametal taken from thegroup consisting of lithium, sodium, potassium, magnesium, calcium,barium and strontium inthe presence of an aqueous liquid, subsequentlyadding to the batcha granular organic solid, shaping the mass, dryingand firing at an elevated temperature.

6. The method of making a refractorystructure of high porosity whichcomprises thoroughly-mixing zircon with a permanent bonding agentincluding phosphoric acid and adouble silicate of zirconium and a. metaltakenfrom the group con-. sisting of lithium, sodium, potassium,magnesium, calcium, barium and strontium and. a green strength bondingagent in the presence of an aqueousv liquid, subsequently adding tothe'batch a granular organic solid, shaping the: mass, drying and firingat an elevated temperature.

7. The method of making a refractory structure of highporosity whichcomprises thoroughly mixing zircon with apermanent bonding agentincluding phosphoric acid and a double silicateof zirconium and a metaltaken from the group consisting of lithium, sodium, potassium,magnesium, calcium, barium and strontium and a green strength bondingagent in the presence of an aqueous liquid, subsequently adding to thebatch a. granular organic solid having particle sizes larger than theparticle sizes of said zircon: and said bonding agent,shaping the mass,drying and firing at an elevated temperature under. good oxidizingconditions.

' CHARLES J. KINZIE.

EUGENE WAINER.

